Expandable vermiculite and other expandable phyllosilicate compounds are distinguished by their high heat resistance, the good insulating and sealing properties and find use primarily as packaging and absorption materials. Moreover, as intumescing additives in fire-retarding products, they offer a decisive advantage over conventional expandable graphite materials because of their incombustibility.
Expandable phyllosilicates, such as vermiculite, are built up from octahedral and tetrahedral layers, between which exchangeable cations, such as magnesium and aluminum cations are intercalated, the proportions of which vary depending on the origin of the phyllosilicate. Because of the presence of interlayer water, such expandable phyllosilicates are subject to expansion when heated because the interlayer water is released spontaneously at higher temperatures, so that the layers are forced apart. The temperature, at which the expansion process sets in, is referred to as the onset temperature, which is at 320° C., for example, in the case of native, expandable vermiculite, as used in the following comparison example.
Such expandable phyllosilicates, like expandable graphite, are used because of this thermal expansion behavior as intumescing fire-retarding additives for the production of fire-retarding compositions, for example, for the fire-retarding sealing of through holes, wall bushings and other openings in walls, floors and/or corners of buildings. In the event of a fire, the expandable phyllosilicate, present in the fire-retarding composition, expands so that, after the matrix material of the flame-retarding composition has been burned away, the opening, which is to be sealed, remains closed for a further period of time due to the expansion of the phyllosilicate.
Depending on the nature of the pipe wall bushings, such fire-retarding bulkhead systems must satisfy different requirements. For example, in the case of the very rapidly melting and combusting polyurethane pipes, the resulting opening must be closed within a very short time. This requires the intumescing material to have a high expansion rate and a large expansion volume. Accordingly, as in the case of the onset temperature, a high measure of variability is required with regard to these parameters also, for example, in order to be able to adjust the expansion behavior of the intumescing fire-retarding materials selectively to the special product requirement for the production of such fire-retarding materials. In contrast to expandable graphite, which has previously been used as the standard intumescing material, but is burned oxidatively at high temperatures, the expandable phyllosilicates, such as vermiculite, are distinguished by their high thermal stability. However, in native form, these expandable phyllosilicates have only a moderate pressure-increasing expansion behavior, which greatly limits the use of these materials in passive fire protection.
However, due to the limited selection of intercalate compounds (guest), the variations of the expansion properties, particularly of the expansion volume and of the onset temperature, of the commercially obtainable phyllosilicates is limited. However, in order to be able to react flexibly to the special product requirements, especially in the area of passive fire protection, expandable phyllosilicate-intercalation compounds are required, which make possible a higher range of variation and a selective adjustment of their intumescing properties, especially with regard to the expansion volume and the onset, that is, the temperature at which expansion commences.
The modification of expandable phyllosilicates by intercalating guest molecules is already known and is usually carried out by dispersing silicate particles in a solution of the corresponding guest compound. Inorganic salts as well as organic compounds can be intercalated as guest molecules. The onset temperature of commercially available phyllosilicates is about 300° C.
For example, U.S. Pat. No. 4,305,992 describes an intumescing sheet material with a greatly reduced negative expansion behavior, which contains an expandable vermiculite with a particle size of about 0.1 mm to 6 mm, the onset temperature of which has been adjusted by cationic exchange with ammonium phosphate, ammonium carbonate, ammonium acetate, ammonium hydroxide and urea to a temperature, significantly lower than that of conventional vermiculites.
U.S. Pat. No. 5,079,280 and the corresponding European patent application 0 429 246 disclose vermiculite, which can be expanded at a low temperature, and intumescing sheet material, which contains this vermiculite. In this case, the expansion temperature is lowered by intercalating a potassium nitrate solution. Ammonium nitrate, potassium chloride and ammonium chloride are also given as intercalation compound, but are presented as less effective.
U.S. Pat. No. 5,116,537 describes a method for lowering the onset temperature and for improving the expansion properties of vermiculite also with a potassium nitrate solution.
Finally, U.S. Pat. No. 5,326,500 discloses a vermiculite with improved expansion behavior, which was modified by intercalating lithium cations, (C2-C6) alkylammonium cations, allylammonium cations or ammonium (C3-C6) alkylcarboxylic acids.
However, the expandable phyllosilicates, obtained by this state of the art, are not completely satisfactory, because selective matching of the properties of the intumescing fire-retarding additive to the receptive binder matrix of the fire-retarding material cannot be achieved. As already stated above, melting metal and plastic pipes must be squeezed off in the case of passive fire protection by the expanding process of the intumescing materials, in order to close off the cavity, formed by the shrinking process of the pipe wall bushings, quickly once again with formation of a mechanically stable and thermally insulating protective layer. For this purpose, intumescing materials with a pressure-increasing expansion are required, for which the expansion process does not terminate in spite of the resistance or counter pressure, as is it does in the case of the reaction of carbon donors (such as starch and pentaerythritol), acid donors (such as ammonium polyphosphate) and blowing agents (such as melamine).
Moreover, the expansion process may set in only when the binder matrix of the fire-retarding composition has softened, since only then a synergistic effect and the best possible efficiency of the pressure-increasing expansion of the expandable phyllosilicate can be attained. It is therefore necessary to have available expandable phyllosilicates, the properties profile of which can be adjusted selectively and more accurately with respect to the expansion behavior. In this connection, it is particularly important to be able to modify the onset temperature in the desired manner at elevated expansion rates.